ACI 318 ordinary shear wall

[TehMightyEngineer]

A couple of quick questions.

First, does anyone know of a good example for an ordinary shear wall designed per ACI 318 per section 11.9? I can find a bunch of examples for special shear walls per section 21 for seismic but the only example I can find for an ordinary shear wall is in the 2nd edition of the PCA book "Seismic and Wind Design of Concrete Buildings, 2nd Edition" but that only uses ACI 318-02 and their equations are vastly different than 318-08 and 318-12.

Second, and if an example can't be found, can someone clarify their use of Mu (factored moment). This is used in equation 11-28 in section 11.9.6. I take this to be the factored out-of-plane moment in the shear wall but I question wither they mean the overturning moment in-plane with the shear wall. Can someone clarify this as ACI 318 is extremely unclear on what Mu actually means.

Maine EIT, Civil/Structural. Going to take the 1st part of the 16-hour SE test in April, wish me luck!

 

[TehMightyEngineer]

Ah, I believe I can answer my own question.

I found an example in "Reinforced Concrete Mechanics and Design, 4th Edition" by MacGregor and Wight. Example 19-14 covers design of a shear wall for wind loads per ACI 318 section 11 and uses up to date equations. Excellent.

It appears, if I read this correctly, that Mu is indeed the in-plane moment on the shear wall. Not the out-of-plane moment that I had previously thought.

Maine EIT, Civil/Structural. Going to take the 1st part of the 16-hour SE test in April, wish me luck!

 

[ChrisMagadiaCom]

Mu is the inplane moment of the bending moment towards the strong direction of the wall in plan

regards
chris magadia

http://www.chrismagadia.com

ChrisMagadia.Com - The Structural Engineers' Forum and Resources Website. Civilizations owe its existence to Structural Engineering. Do you Agree?

 

[TehMightyEngineer]

@Chris: Thanks, it's good to have confirmation.

Maine EIT, Civil/Structural. Going to take the 1st part of the 16-hour SE test in April, wish me luck!

 

[bridget13]

Is there any case where a "shear wall" can be designed for out-of-plane moments?, please give an example.

 

[TehMightyEngineer]

Are you asking "can it be designed successfully for out of plane loads" or "can a shear wall have out of plane loads"? The short answer is yes to both. Out of plane moments in a wall are just like moments in a floor slab when you take things down to their most basic level. You have to include compression and the potential for both shear and out of plane loads simultaneously of course. Imagine an exterior wall with roof joists attached to one side of the wall. Throw in some snow and a quartering wind and you have shear and out of plane loads.

Maine EIT, Civil/Structural. Going to take the 1st part of the 16-hour SE test in April, wish me luck!

 

[johnbridge231]

Sure it can! A rectangular cross section can take bending moments acting about both directions. This is called biaxial bending. In case of walls, one dimension is greater than the other, a fact that affactes the corresponding stiffness in both directions. So, as the stiffness is greater in one direction, the moments are significant in that direction only. But if you want to calculate in a rigorous way, you can check the cross section of the wall against out-of-plane moments as well. In this case you will need specialized software.
Regards.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[TehMightyEngineer]

You can do it by hand, it's just very complicated.

Maine EIT, Civil/Structural. Going to take the 1st part of the 16-hour SE test in April, wish me luck!

 

[pkjr618]

I have tried modet the wall as a stick model in ETABS. However, the auto-design process might not be applicable since the stick model is considered as a column and not a wall. You would have to design the wall manually using the forces from the analysis.

 

[MrHershey]

Shear walls are typically modeled as area (I usually use shell) elements in ETABS. From there you can use the autodesign.